1. Field of the Invention
The present invention generally relates to a rubber composition and particularly to such a composition which provides a rubber having high hardness, set resistance and hydrolysis resistance.
2. Related Art Statement
A rubber used for producing various sorts of vibration isolators and a stabilizer bushing for an automotive vehicle, is required to possess (i) high hardness, (ii) appropriate rubber elasticity and accordingly suitable set resistance, (iii) good weather resistance, and additionally (iv) excellent slide characteristic.
For obtaining a rubber having a sufficiently high degree of hardness, in particular, it is generally preferred to select urethane rubber. However, urethane rubber suffers from low hydrolysis resistance and therefore insufficiently low weather resistance. There have been some proposals to provide a high-hardness polymer rubber free from the problem of low hydrolysis resistance. For example, unexamined Japanese Patent Application laid open under Publication No. 1(1989)-306440 discloses a high-strength rubber obtained by mixing zinc methacrylate with a rubber material and crosslinking the mixture with an organic peroxide. However, even this rubber does not have appropriate slide characteristic.
Meanwhile, for obtaining a rubber having excellent slide characteristic, it is preferred to select a self-lubricating rubber containing silicone oil. However, such a self-lubricating rubber suffers from low hardness. Self-lubricating thermoplastic urethane rubber lacks appropriate set resistance and hydrolysis resistance, and self-lubricating thermosetting urethane rubber lacks appropriate hydrolysis resistance.
Thus, there is known no rubber that satisfies the requirements to hardness, set resistance, hydrolysis resistance, and slide characteristic.